Structure and function of lymphatics.

Lymphatics are large vessels with a lumen potentially ten times wider than blood vessels and have a mean mesh diameter in the upper dermis of approximately 504 +/- 88 microns. The plexus lies just deep to the subpapillary venous plexus and when functioning well it is difficult to identify because of the attenuated endothelium and collapsed lumen. The role of the lymphatic as a pathway for the Langerhans cell and as an exit for macromolecules such as lipid and protein make it an essential organ for normal skin biology. When this system fails, impaired immunity, fibrosis, and recurrent infections are inevitable. Even vasculitis may be a consequence of failure of clearance of immune complexes from the interstitium. The adipose tissue and deep dermis are especially vulnerable in this respect. Elastin fibers support cutaneous lymphatics and may be low resistance pathways through the connective tissues into the lymphatic. Identification of lymphatics by special markers is a concept that currently fails to take into account that changing roles in disease may be associated with a change in the specificity of markers. The anatomy of lymphatic vessels in the skin is described and the role of the lymphatic is emphasized.